Integrated HFC trans-1234ze manufacture process

ABSTRACT

An integrated process for the manufacture of HFO trans-1,3,3,3-tetrafluoropropene (HFO trans-1234ze) by first catalytically dehydrofluorinating 1,1,1,3,3-pentafluoropropane to thereby produce a mixture of cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally recovering hydrogen fluoride, catalytically isomerizing cis-1234ze into trans-1234ze, and recovering trans-1,3,3,3-tetrafluoropropene.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.11/657,354 filed Jan. 24, 2007, now U.S. Pat. No. 7,485,760, which isincorporated herein by reference, and which claims the benefit of U.S.Provisional patent application Ser. No. 60/839,874 filed Aug. 24, 2006,also incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention pertains to an integrated process for the manufacture oftrans-1,3,3,3-tetrafluoropropene (HFO trans-1234ze). More particularly,the invention pertains to a process for the manufacture of the HFOtrans-1234ze by first catalytically dehydrofluorinating1,1,1,3,3-pentafluoropropane to thereby produce a mixture ofcis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene andhydrogen fluoride. Then optionally recovering hydrogen fluoride,catalytically isomerizing cis-1234ze into trans-1234ze, and recoveringtrans-1,3,3,3-tetrafluoropropene. The integration of an isomerizationreactor charged with a suitable isomerization catalyst helps to convertcis-1234ze into its trans-isomer, which allows increasing thesingle-pass yield of trans-1234ze.

Chlorofluorocarbons (CFCs) like trichlorofluoromethane anddichlorodifluoromethane have been used as refrigerants, blowing agentsand diluents for gaseous sterilization. In recent years, there has beenwidespread concern that certain chlorofluorocarbons might be detrimentalto the Earth's ozone layer. As a result, there is a worldwide effort touse halocarbons which contain fewer or no chlorine substituents.Accordingly, the production of hydrofluorocarbons, or compoundscontaining only carbon, hydrogen and fluorine, has been the subject ofincreasing interest to provide environmentally desirable products foruse as solvents, blowing agents, refrigerants, cleaning agents, aerosolpropellants, heat transfer media, dielectrics, fire extinguishingcompositions and power cycle working fluids. In this regard,trans-1,3,3,3-tetrafluoropropene (trans-1234ze) is a compound that hasthe potential to be used as a zero Ozone Depletion Potential (ODP) and alow Global Warming Potential (GWP) refrigerant, blowing agent, aerosolpropellant, solvent, etc, and also as a fluorinated monomer.

It is known in the art to produce HFO-1234ze (i.e.HydroFluoroOlefin-1234ze). For example, U.S. Pat. No. 5,710,352 teachesthe fluorination of 1,1,1,3,3-pentachloropropane (HCC-240fa) to formHCFC-1233zd and a small amount of HFO-1234ze. U.S. Pat. No. 5,895,825teaches the fluorination of HCFC-1233zd to form HFC-1234ze. U.S. Pat.No. 6,472,573 also teaches the fluorination of HCFC-1233zd to formHFO-1234ze. U.S. Pat. No. 6,124,510 teaches the formation of cis andtrans isomers of HFO-1234ze by the dehydrofluorination of HFC-245fa inthe presence of an oxygen-containing gas using either a strong base or achromium-based catalyst. European patent EP 0939071 describes theformation of HFC-245fa via the fluorination of HCC-240fa throughintermediate reaction product which is an azeotropic mixture ofHCFC-1233zd and HFO-1234ze.

It has been determined that these known processes are not economicalrelative to their product yield. It has also been noted that asignificant amount of cis-1234ze is generated together with itstrans-isomer in these know processes. Hence, there is a need for meansby which trans-1234ze can be isolated from product mixtures andcis-1234ze can be either recycled via its fluorination to HFC-245fa ormore preferably converted into trans-1234ze. Accordingly, the presentinvention provides an integrated process for producing trans-1234ze fromwhich highly pure trans-1234ze can be obtained at a higher yield thanprior art processes and cis-1234ze can be isomerized into trans-1234zein contrast to known processes. In particular, it has now been foundthat trans-1234ze may be formed by dehydrofluorinating1,1,1,3,3-pentafluoropropane in the absence of an oxygen-containing gasto produce a mixture of cis-1,3,3,3-tetrafluoropropene,trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally,but preferably recovering hydrogen fluoride, catalytically isomerizingcis-1234ze into trans-1234ze, and then recoveringtrans-1,3,3,3-tetrafluoropropene. Unconverted cis-1234ze and HFC-245famay then be directly recycled.

DESCRIPTION OF THE INVENTION

The invention provides a process for the production oftrans-1,3,3,3-tetrafluoropropene which comprises:

(a) dehydrofluorinating 1,1,1,3,3-pentafluoropropane to thereby producea result comprising cis-1,3,3,3-tetrafluoropropene,trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride;

(b) optionally recovering hydrogen fluoride from the result of step (a);

(c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropeneinto trans-1,3,3,3-tetrafluoropropene; and

(d) recovering trans-1,3,3,3-tetrafluoropropene.

The invention also provides a continuous, integrated manufacturingprocess for the production of trans-1,3,3,3-tetrafluoropropene whichcomprises:

(a) dehydrofluorinating 1,1,1,3,3-pentafluoropropane conducted as avapor phase reaction to thereby produce a result comprisingcis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene andhydrogen fluoride;

(b) recovering hydrogen fluoride from the result of step (a);

(c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropeneinto trans-1,3,3,3-tetrafluoropropene; and

(d) recovering trans-1,3,3,3-tetrafluoropropene.

The first step of the process involves the catalytic conversion ofHFC-245fa by dehydrofluorinating HFC-245fa to produce a resultcomprising a combination of cis-1,3,3,3-tetrafluoropropene,trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride.Dehydrofluorination reactions are well known in the art. Preferablydehydrofluorination of HFC-245fa is done in a vapor phase, and morepreferably in a fixed-bed reactor in the vapor phase. Thedehydrofluorination reaction may be conducted in any suitable reactionvessel or reactor, but it should preferably be constructed frommaterials which are resistant to the corrosive effects of hydrogenfluoride such as nickel and its alloys, including Hastelloy, Inconel,Incoloy, and Monel or vessels lined with fluoropolymers. These may besingle pipe or multiple tubes packed with a dehydrofluorinating catalystwhich may be one or more of fluorinated metal oxides in bulk form orsupported, metal halides in bulk form or supported, and carbon supportedtransition metals, metal oxides and halides. Suitable catalystsnon-exclusively include fluorinated chromia (fluorinated Cr₂O₃),fluorinated alumina (fluorinated Al₂O₃), metal fluorides (e.g., CrF₃,AlF₃) and carbon supported transition metals (zero oxidation state) suchas Fe/C, Co/C, Ni/C, Pd/C. The HFC-245fa is introduced into the reactoreither in pure form, impure form, or together with an optional inert gasdiluent such as nitrogen, argon, or the like. In a preferred embodimentof the invention, the HFC-245fa is pre-vaporized or preheated prior toentering the reactor. Alternatively, the HFC-245fa is vaporized insidethe reactor. Useful reaction temperatures may range from about 100° C.to about 600° C. Preferred temperatures may range from about 150° C. toabout 450° C., and more preferred temperatures may range from about 200°C. to about 350° C. The reaction may be conducted at atmosphericpressure, super-atmospheric pressure or under vacuum. The vacuumpressure can be from about 5 torr to about 760 torr. Contact time of theHFC-245fa with the catalyst may range from about 0.5 seconds to about120 seconds, however, longer or shorter times can be used.

In the preferred embodiment, the process flow is in the down or updirection through a bed of the catalyst. It may also be advantageous toperiodically regenerate the catalyst after prolonged use while in placein the reactor. Regeneration of the catalyst may be accomplished by anymeans known in the art, for example, by passing air or air diluted withnitrogen over the catalyst at temperatures of from about 100° C. toabout 400° C., preferably from about 200° C. to about 375° C., for fromabout 0.5 hour to about 3 days. This is followed by either HF treatmentat temperatures of from about 25° C. to about 400° C., preferably fromabout 200° C. to about 350° C. for fluorinated metal oxide catalysts andmetal fluoride ones or H₂ treatment at temperatures of from about 100°C. to about 400° C., preferably from about 200° C. to about 350° C. forcarbon supported transition metal catalysts.

In an alternative embodiment of the invention, dehydrofluorination ofHFC-245fa can also be accomplished by reacting it with a strong causticsolution that includes, but is not limited to KOH, NaOH, Ca(OH)₂ and CaOat an elevated temperature. In this case, the caustic strength of thecaustic solution is of from about 2 wt. % to about 100 wt. %, morepreferably from about 5 wt. % to about 90 wt. % and most preferably fromabout 10 wt. % to about 80 wt. %. The reaction may be conducted at atemperature of from about 20° C. to about 100° C., more preferably fromabout 30° C. to about 90° C. and most preferably from about 40° C. toabout 80° C. As above, the reaction may be conducted at atmosphericpressure, super-atmospheric pressure or under vacuum. The vacuumpressure can be from about 5 torr to about 760 torr. In addition, asolvent may optionally be used to help dissolve the organic compounds inthe caustic solution. This optional step may be conducted using solventsthat are well known in the art for said purpose.

Optionally but preferably, hydrogen fluoride is then recovered from theresult of the dehydrofluorination reaction. Recovering of hydrogenfluoride is conducted by passing the composition resulting from thedehydrofluorination reaction through a sulfuric acid extractor to removehydrogen fluoride, subsequently desorbing the extracted hydrogenfluoride from the sulfuric acid, and then distilling the desorbedhydrogen fluoride. The separation may be conducted by adding sulfuricacid to the mixture while the mixture is in either the liquid or gaseousstates. The usual weight ratio of sulfuric acid to hydrogen fluorideranges from about 0.1:1 to about 100:1. One may begin with a liquidmixture of the fluorocarbons and hydrogen fluoride and then add sulfuricacid to the mixture.

The amount of sulfuric acid needed for the separation depends on theamount of HF present in the system. From the solubility of HF in 100%sulfuric acid as a function of a temperature curve, the minimumpractical amount of sulfuric acid can be determined. For example at 30°C., about 34 g of HF will dissolve in 100 g of 100% sulfuric acid.However, at 100° C., only about 10 g of HF will dissolve in the 100%sulfuric acid. Preferably the sulfuric acid used in this invention has apurity of from about 50% to 100%.

In the preferred embodiment, the weight ratio of sulfuric acid tohydrogen fluoride ranges from about 0.1:1 to about 1000:1. Morepreferably the weight ratio ranges from about 1:1 to about 100:1 andmost preferably from about 2:1 to about 50:1. Preferably the reaction isconducted at a temperature of from about 0° C. to about 100° C., morepreferably from about 0° C. to about 40° C., and most preferably fromabout 20° C. to about 40° C. The extraction is usually conducted atnormal atmospheric pressure, however, higher or lower pressureconditions may be used by those skilled in the art. Upon adding thesulfuric acid to the mixture of fluorocarbons and HF, two phases rapidlyform.

An upper phase is formed which is rich in the fluorocarbons and a lowerphase which is rich in HF/sulfuric to acid. By the term “rich” is meant,the phase contains more than 50% of the indicated component in thatphase, and preferably more than 80% of the indicated component in thatphase. The extraction efficiency of the fluorocarbon can range fromabout 90% to about 99%.

After the separation of the phases, one removes the upper phase rich inthe fluorocarbons from the lower phase rich in the hydrogen fluoride andsulfuric acid. This may be done by decanting, siphoning, distillation orother techniques well known in the art. One may optionally repeat thefluorocarbon extraction by adding more sulfuric acid to the removedlower phase. With about a 2.25:1 weight ratio of sulfuric acid tohydrogen fluoride, one can obtain an extraction efficiency of about 92%in one step. Preferably one thereafter separates the hydrogen fluorideand sulfuric acid. One can take advantage of the low solubility of HF insulfuric at high temperatures to recover the HF from sulfuric. Forexample, at 140° C., only 4 g of HF will dissolve in 100% sulfuric acid.One can heat the HF/sulfuric acid solution up to 250° C. to recover theHF. The HF and sulfuric acid may then be recycled. That is, the HF maybe recycled to a preceding reaction for the formation of the HFC-245faand the sulfuric acid may be recycled for use in further extractionsteps.

In another embodiment of the invention, the recovering of hydrogenfluoride from the mixture of fluorocarbon and hydrogen fluoride may beconducted in a gaseous phase by a continuous process of introducing astream of sulfuric acid to a stream of fluorocarbon and hydrogenfluoride. This may be conducted in a standard scrubbing tower by flowinga stream of sulfuric acid countercurrent to a stream of fluorocarbon andhydrogen fluoride. Sulfuric acid extraction is described, for example inU.S. Pat. No. 5,895,639, which is incorporated herein by reference.

Alternatively, HF can be recovered or removed by using water or causticscrubbers, or by contacting with a metal salt. When water extractor isused, the technique is similar to that of sulfuric acid. When caustic isused, HF is just removed from system as a fluoride salt in aqueoussolution. When metal salt (e.g. potassium fluoride, or sodium fluoride)is used, it can be used neat or in conjunction with water. HF can berecovered when metal salt is used.

Then at least a portion of the cis-1,3,3,3-tetrafluoropropene isisomerized into trans-1,3,3,3-tetrafluoropropene. A stream ofcis-1,3,3,3-tetrafluoropropene or its mixture withtrans-1,3,3,3-tetrafluoropropene and/or 1,1,1,3,3-pentafluoropropane isfed into an isomerization reactor which contains a suitableisomerization catalyst (e.g., fluorinated metal oxides in bulk orsupported, metal fluorides in bulk or supported, carbon supportedtransition metals, etc.) to convert most of the cis-1234ze intotrans-1234ze. The isomerization reaction may be conducted in anysuitable reaction vessel or reactor, but it should preferably beconstructed from materials which are resistant to corrosion such asnickel and its alloys, including Hastelloy, Inconel, Incoloy, and Monelor vessels lined with fluoropolymers. These may be single pipe ormultiple tubes packed with an isomerization catalyst which may be afluorinated metal oxide, metal fluoride, or a carbon supportedtransition metal. Suitable catalysts non-exclusively include fluorinatedchromia, chromium fluoride, fluorinated alumina, aluminum fluoride, andcarbon supported cobalt. Useful reaction temperatures may range fromabout 25° C. to about 450° C. Preferred temperatures may range fromabout 50° C. to about 350° C., and more preferred temperatures may rangefrom about 75° C. to about 250° C. The reaction may be conducted atatmospheric pressure, super-atmospheric pressure or under vacuum. Thevacuum pressure can be from about 5 torr to about 760 torr. Contact timeof the cis-1,3,3,3-tetrafluoropropene with the catalyst may range fromabout 0.5 seconds to about 120 seconds, however, longer or shorter timescan be used.

Trans-1,3,3,3-tetrafluoropropene may be recovered from the reactionproduct mixture comprised of unreacted starting materials andby-products, including cis-1,3,3,3-tetrafluoropropene and anyby-products and/or starting materials by any means known in the art,such as by extraction and preferably distillation. The mixture oftrans-1,3,3,3-tetrafluoropropene, unconvertedcis-1,3,3,3-tetrafluoropropene, unreacted HFC-245fa and any by-productsare passed through a distillation column. For example, the distillationmay be preferably conducted in a standard distillation column atatmospheric pressure, super-atmospheric pressure or a vacuum. Preferablythe pressure is less than about 300 psig, more preferably less thanabout 150 psig and most preferably less than 100 psig. The pressure ofthe distillation column inherently determines the distillation operatingtemperature. Trans-1,3,3,3-tetrafluoropropene has a boiling point ofabout −19° C.; cis-1,3,3,3-tetrafluoropropene has a boiling point ofabout 9° C.; HFC-245fa has a boiling point of about 15° C.Trans-1,3,3,3-tetrafluoropropene may be recovered as distillate byoperating the distillation column at from about −10° C. to about 90° C.,preferably from about 0° C. to about 80° C. Single or multipledistillation columns may be used. The distillate portion includessubstantially all the trans-1,3,3,3-tetrafluoropropene. The bottomstream of the distillation includes cis-1,3,3,3-tetrafluoropropene,HFC-245fa, a small amount of unrecovered HF and as well as any otherimpurities. Optionally, the residual amounts of HF/HCl present in thebottom distillate are removed by passing through a water/causticscrubber, and followed by a sulfuric acid drying column. The bottomstream is then further distilled by using another distillation column.The mixture of cis-1234ze and HFC-245fa is recovered as a distillate,which is then recycled back to HFC-245fa dehydrofluorination reactor.

In the following alternative embodiments of the invention, the HFC-245fadehydrofluorination reactor and the cis-1234ze isomerization reactor canbe combined or independent. The trans-1234ze isolation can be after orbefore the cis-1234ze isomerization reaction.

Alternative 1

(1) Combined reaction of HFC-245fa dehydrofluorination and cis-1234zeisomerization in one reaction vessel.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze. Optionally, the remaining mixture isrecycled back to step 1.

Alternative 2

(1) Catalytic dehydrofluorination of HFC-245fa into a compositioncomprising trans/cis-1234ze.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze wherein the outlet stream of (2) feedsinto a distillation column. The product, trans-1234ze, is isolated as adistillate from the rest of the mixture, i.e. cis-1234ze, the un-reactedHFC-245fa and other minor by-products. The residual amounts of HF/HClpresent in the distillate are removed, and followed by a drying step.The bottom stream from the distillation of (3) is split to two streamsand fed to steps (4) and (1), respectively. Optionally, furtherdistillation is conducted by using another distillation column afterstep (3). In this distillation column, the mixture of cis-1234ze andHFC-245fa is recovered as a distillate, which is subsequently fed tostep (4). The bottom stream from this 2^(nd) distillation column isrecycled back to step (1).(4) Catalytic isomerization of cis-1234ze.

The mixture of cis-1234ze/HFC-245fa from step (3) is fed into anisomerization reactor which contains a suitable isomerization catalystto convert most of the cis-1234ze into trans-1234ze. The effluent fromthe catalytic reactor of step (4) is fed into step (3) for trans-1234zeisolation.

Alternative 3

(1) Catalytic dehydrofluorination of 245fa into trans/cis-1234ze.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze

(4) Catalytic isomerization of cis-1234ze wherein the mixture comprisingcis-1234ze and 245fa from step (3) is fed into an isomerization reactorwhich contains a suitable isomerization catalyst to convert most of thecis-1234ze into trans-1234ze.

(5) Isolation of trans-1234ze wherein the effluent from step (4) is fedinto a distillation column. The product, trans-1234ze, is isolated as adistillate from the rest of the mixture, i.e. cis-1234ze, the un-reacted245fa and other minor by-products. The bottom stream from thedistillation of (5) is recycled back to step (1).

The following non-limiting examples serve to illustrate the invention.

Example 1 HFC-245fa Dehydrofluorination Over Selected Catalysts

Three different kinds of catalysts, namely, fluorinated metal oxide,metal fluoride(s), and supported metal, were used for 245fadehydrofluorination in Example 1. In each case, 20 cc of catalyst wasused. A 100% 245fa feed was flowed over catalyst at a rate of 12 g/h. Asshown in Table 1, all the catalysts listed in Table 1 exhibited a highactivity (>80% 245fa conversion) and a high selectivity tocis/trans-1234ze (>90%) during 245 dehydrofluorination.

TABLE 1 HFC-245fa dehydrofluorination over various catalysts trans-trans- temp HFC-245fa 1234ze cis-1234ze selectivity 1234ze catalyst ° C.conversion % selectivity % selectivity % for others* % lbs/hr/ft³Fluorinated 350 96.0 80.6 18.0 1.4 26.0 Cr₂O₃ AlF₃ 350 96.8 80.4 16.33.3 26.2 10% MgF₂—90% 350 98.3 78.6 17.5 4.0 26.0 AlF₃ 0.5 wt % 525 80.067.8 23.4 8.8 18.2 Fe/AC Reaction conditions: 20 cc catalyst, 12 g/h245fa, 1 atm. *Others include 2,3,3,3-tetrafluoropropene,3,3,3-trifluoropropyne, etc.

Example 2 Isomerization of Cis-1234ze Over Selected Catalysts

Three different kinds of catalysts, namely, fluorinated metal oxide,metal fluoride(s), and supported metal, were used for cis-1234zeisomerization in Example 2. In each case, 20 cc of catalyst was used. Amixture of 85.3% cis-1234ze/14.7% 245fa was flowed over catalyst at arate of 12 g/h. For a specified catalyst, a suitable reactiontemperature was carefully chosen such that almost no dehydrofluorinationreaction occurs to the HFC-245fa included in the feed. As shown in Table2, all the catalysts except 0.5 wt % Co/AC listed in Table 2 provided ahigh activity (>80% cis-1234ze conversion) and a high selectivity totrans-1234ze (>95%) during cis-1234ze isomerization. The 0.5 wt % Co/ACcatalyst exhibited a moderate activity (45% of cis-1234ze conversion)and a high selectivity to trans-1234ze (about 98%).

TABLE 2 Isomerization of cis-1234ze over various catalysts reactiontemp. conversion, % selectivity, % catalyst (° C.) cis-1234zetrans-1234ze Fluorinated Cr₂O₃ 100 91.0 100.0 AlF₃ 200 85.2 99.3 0.5 wt% Co/AC 350 45.0 98.2 Reaction conditions: 20 cc catalyst, 12 g/h 85.3%cis-1234ze/14.7% 245fa, 1 atm

Example 3 Cis-1234ze Isomerization in the Presence of HF OverFluorinated Cr₂O₃

In this example, the product stream from Reactor 1 in which 245fadehydrofluorination reaction was conducted over a fluorinated Cr₂O₃catalyst at 350° C. was introduced into Reactor 2 which was also chargedwith a fluorinated Cr₂O₃ catalyst to conduct cis-1234ze isomerizationreaction at 100 or 200° C. in the presence of HF (which was formedduring 245fa dehydrofluorination in Reactor 1). Table 3 shows thecompositions of exit gases of the two reactors. At 100° C., the molepercentage of trans-1234ze was slight higher in the exit gas of Reactor2 than that in the exit gas of Reactor 1, while the mole percentage ofcis-1234ze was slightly lower and the mole percentage of 245fa was aboutthe same. As a result the mole ratio of trans-1234ze to cis-1234zw wasslightly increased (e.g., from 3.96 to 4.36 after 1 h on stream) afterisomerization reaction, indicating small amount of cis-1234 wasconverted into trans-1234ze through isomerization in Reactor 2. At 200°C., the mole percentages of both trans-1234ze and cis-1234ze weresignificantly lower in the exit gas of Reactor 2 than those in the exitgas of Reactor 1, while the mole percentage of 245fa was significantlyhigher. This indicates the occurrence of hydrofluorination reactionbetween c/t-1234ze and HF. These results suggest that the HF bepreferably removed from the mixture before feeding into isomerizationreactor in order to avoid the hydrofluorination of trans/cis-1234ze to245fa and increase the conversion of cis-1234ze to trans-1234ze.

TABLE 3 The compositions of exit gases of the two reactors Rx 1 Rx 2mol, % mol, % t Temp trans/cis trans- cis- HFC- Temp. trans/cis t- c-(h) (° C.) ratio 1234ze 1234ze 245fa others* (° C.) ratio 1234ze 1234ze245fa others* 1 350 3.96 69.3 17.5 3.2 10.0 100 4.36 70.5 16.2 3.2 10.12 350 3.94 71.7 18.2 2.5 7.6 100 4.22 72.5 17.2 2.4 7.8 3 350 3.87 73.118.9 2.1 5.8 100 4.25 73.7 17.3 2.1 7.0 4 350 3.86 73.2 19.0 2.2 5.6 2006.06 55.2 9.1 29.4 6.3 5 350 3.86 73.3 19.0 2.2 5.2 200 5.94 38.2 6.451.8 3.6 *Others include 2,3,3,3-tetrafluoropropene,3,3,3-trifluoropropyne, etc.

Example 4 Combined HFC-245fa Dehydrofluorination and Cis-1234zeIsomerization

Two different kinds of catalysts, namely, fluorinated metal oxide andmetal fluoride, were used for the combined reaction in Example 4. Ineach case, 20 cc of catalyst was used. A mixture of 8.2% ofcis-1234ze/91.8% of HFC-245fa was flowed over catalyst at a rate of 12g/h. For a specified catalyst, a suitable reaction temperature wascarefully chosen such that both the HFC-245fa dehydrofluorination andthe cis-1234ze isomerization can take place at the same time. TheHFC-245fa conversion and trans-1234ze selectivity during the combinedreaction was calculated assuming cis-1234ze remains unchanged before andafter reaction. As shown in Table 4, the nominal trans-1234zeselectivity was about 94%, which was much higher than that in thereaction of HFC-245fa dehydrofluorination. This result indicates theoccurrence of cis-1234ze isomerization to trans-1234ze during thecombined reaction with cis-1234ze/HFC-245fa mixture as feed. Thisexample demonstrated that under optimal operation temperature theHFC-245fa dehydrofluorination and the cis-1234ze isomerization can beconducted simultaneously over the same catalyst in the same reactor.

TABLE 4 Combined HFC-245fa dehydrofluorination and cis-1234zeisomerization temp. HFC-245fa trans-1234ze trans-1234ze catalyst (° C.)conversion, % selectivity, % lbs/hr/ft³ Fluorinated 250 77.5 93.5 22.5Cr₂O₃ AlF₃ 250 81.7 94.2 23.9 Reaction conditions: 20 cc catalyst, 12g/h 8.2% cis-1234ze/91.8% HFC-245fa, 1 atm

These examples demonstrate that the selected catalysts are, indeed,active for the dehydrofluorination of HFC-245fa to cis/trans-1234ze andthe isomerization of cis-1234ze to trans-1234ze.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. It is intended that the claims be interpreted to coverthe disclosed embodiment, those alternatives which have been discussedabove and all equivalents thereto.

1. A process for the production of trans-1,3,3,3-tetrafluoropropenewhich comprises: (a) dehydrofluorinating 1,1,1,3,3-pentafluoropropane tothereby produce a result comprising cis-1,3,3,3-tetrafluoropropene,trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride; (b) optionallyrecovering hydrogen fluoride from the result of step (a); (c)isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropeneinto trans-1,3,3,3-tetrafluoropropene, forming a remaining mixture; and(d) recovering trans-1,3,3,3-tetrafluoropropene from the remainingmixture, and then recycling the remaining mixture to step (a).
 2. Theprocess of claim 1 further comprising the subsequent step of recoveringcis-1,3,3,3-tetrafluoropropene, or a mixture ofcis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane afterstep (d) and recycling cis-1,3,3,3-tetrafluoropropene or a mixturecis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane back tostep (a) or step (a) and (c).
 3. The process of claim 1 wherein the stepof recovering hydrogen fluoride from the result of step (a) isconducted.
 4. The process of claim 1 wherein steps (a) and (c) areconducted independently.
 5. The process of claim 1 wherein steps (a) and(c) are combined and conducted as a single process step.
 6. The processof claim 1 wherein step (d) is conducted after step (c).
 7. The processof claim 1 wherein step (d) is conducted after step (a) but before step(c).
 8. The process of claim 1 wherein step (d) is conducted after step(a) but before step (c); and then step (d) is then repeated after step(c).
 9. The process of claim 1 wherein trans-1,3,3,3-tetrafluoropropeneis recovered by distillation.
 10. The process of claim 1 wherein step(d) is conducted by distilling the result of step (c) and recoveringtrans-1,3,3,3-tetrafluoropropene as a distillate and a residuecomprising one or more of hydrogen fluoride,cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane.
 11. Theprocess of claim 10 further comprising the subsequent step of removinghydrogen fluoride from the residue.
 12. The process of claim 10 furthercomprising the subsequent step of removing hydrogen fluoride from theresidue by passing the residue through a scrubber comprising water and acaustic, followed by a drying step.
 13. The process of claim 10 furthercomprising the subsequent step of recovering at least one ofcis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane from theresidue and recycling at least one of the recoveredcis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane back tostep (a).
 14. The process of claim 1 wherein the dehydrofluorinating isconducted as a vapor phase reaction.
 15. The process of claim 1 whereinthe dehydrofluorinating is conducted by reacting the1,1,1,3,3-pentafluoropropane with a strong caustic solution.
 16. Theprocess of claim 1 wherein the dehydrofluorinating is conducted with acatalyst comprising one or more of fluorinated metal oxides, metalfluorides, in bulk form or supported and carbon supported transitionmetals.
 17. The process of claim 1 wherein the recovering of hydrogenfluoride is conducted by passing the composition through a sulfuric acidextractor to remove hydrogen fluoride, subsequently desorbing theextracted hydrogen fluoride from the sulfuric acid, and then distillingthe desorbed hydrogen fluoride.
 18. The process of claim 1 wherein theisomerizing is conducted in an isomerizing reactor in the presence of anisomerizing catalyst.
 19. The process of claim 1 wherein the isomerizingis conducted in an isomerizing reactor in the presence of an isomerizingcatalyst comprising one or more of fluorinated metal oxides, metalfluorides, in bulk form or supported and carbon supported transitionmetals.
 20. A continuous, integrated manufacturing process for theproduction of trans-1,3,3,3-tetrafluoropropene which comprises: (a)dehydrofluorinating 1,1,1,3,3-pentafluoropropane conducted as a vaporphase reaction to thereby produce a result comprisingcis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene andhydrogen fluoride; (b) recovering hydrogen fluoride from the result ofstep (a); (c) isomerizing at least a portion of thecis-1,3,3,3-tetrafluoropropene into trans-1,3,3,3-tetrafluoropropene,forming a remaining mixture; and (d) recoveringtrans-1,3,3,3-tetrafluoropropene from the remaining mixture, and thenrecycling the remaining mixture to step (a).
 21. The process of claim 20wherein steps (a) and (c) are conducted independently.
 22. The processof claim 20 wherein steps (a) and (c) are combined and conducted as asingle process step before step (b).
 23. The process of claim 20 whereinstep (d) is conducted after step (c).
 24. The process of claim 20wherein step (d) is conducted after step (a) but before step (c). 25.The process of claim 20 wherein step (d) is conducted after step (a) butbefore step (c); and then step (d) is then repeated after step (c).